Wafer polishing systems are known in the art. They polish the top layer of semiconductor wafers to a desired thickness. To do so, the wafer being polished is immersed in a slurry of water and chemicals during the polishing process. Once the wafer has been polished and washed down, it is placed into an exit station known by some companies as a "water track", after which the wafer is placed into a cassette of wafers. The cassette is maintained within a water bath until full, after which the entire cassette is brought to a cleaning station to remove any chemicals and slurry particles still remaining on the wafers in the cassette and to dry the wafers. After cleaning, the wafers are brought to a measurement station to determine if the polisher produced the desired thickness of their top layers.
FIG. 1, to which reference is now briefly made, illustrates a prior art water track, such as the water track of the #372 Polisher manufactured by IPEC Western Inc. of Phoenix, Ariz., USA. The water track, labeled 10, comprises a frame 12 and a base 14. Frame 12 has jet holes 16 connected to jets (not shown) which emit streams 18 of water through holes 16. Base 14 has holes 20 connected to bubblers (not shown) which bubble small amounts of water 22 through holes 20. When a wafer 25 is dropped into water track 10, pattern-side down, the jets and bubblers are activated. Streams 18, from the water jets, serve to force the wafer 25 in the direction indicated by arrow 24. Small streams 22 push the wafer 25 slightly away from the base 14 and ensure that, while the wafer 25 moves through the track, it never rubs against base 14 and thus, the pattern on the wafer is not scratched.
Other companies produce polishers whose exit stations are formed just of the cassettes. Such a polisher is the 6DS-SP polisher of R. Howard Strasbaugh Inc. San Luis Obispo, Calif., USA.